Spectroscopic and photoluminescence characterization of Dy3+ in Sr0.5Ca0.5TiO3 phosphor

The spectroscopic and photoluminescence characteristics of trivalent dysprosium (Dy³⁺)‐doped Sr_0.5Ca_0.5TiO₃ phosphor materials synthesized via solid‐state reaction method were studied. The X‐ray diffraction profile confirmed the orthorhombic perovskite structure of the prepared samples. Judd–Ofelt analysis was carried out to obtain the intensity parameters and predicted radiative properties of Sr_0.5Ca_0.5TiO₃:2wt%Dy³⁺. The photoluminescence spectrum of Dy³⁺‐doped Sr_0.5Ca_0.5TiO₃ showed three emission peaks at 481, 574 and 638 nm corresponding to ⁴F_9/2→⁶H_15/2, ⁴F_9/2→⁶H_13/2 and ⁴F_9/2→⁶H_11/2 transitions respectively. The variation of luminescence intensity with different excitation wavelengths and Dy³⁺ concentrations is discussed. The decay profiles of ⁴F_9/2 excited levels of Dy³⁺ ions show bi‐exponential behaviour and also a decrease in average lifetime with increase in Dy³⁺ concentration. Yellow to blue luminescence intensity ratio, CIE chromaticity co‐ordinates and correlated color temperature were also calculated for different concentrations of Dy³⁺‐doped Sr_0.5Ca_0.5TiO₃ phosphor at different λ_ex. Copyright © 2015 John Wiley & Sons, Ltd.     

Structural characterization and optical properties of Ca2MgSi2O7:Eu2+,Dy3+ phosphor by solid‐state reaction method

Ca₂MgSi₂O₇:Eu²⁺,Dy³⁺ phosphor was prepared by the solid‐state reaction method under a weak reducing atmosphere. The obtained phosphor was characterized using X‐ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X‐ray spectroscopy (EDX) and Fourier transform infrared (FT‐IR) techniques. The phase structure of the Ca₂MgSi₂O₇:Eu²⁺,Dy³⁺ phosphor was akermanite type, which is a member of the melilite group. The surface morphology of the sintered phosphor was not uniform and phosphors aggregated tightly. EDX and FT‐IR spectra confirm the elements present in the Ca₂MgSi₂O₇:Eu²⁺,Dy³⁺ phosphor. Under UV excitation, a broadband emission spectrum was found. The emission spectra observed in the green region centered at 535 nm, which is due to the 4f–5d transition. The mechanoluminescence (ML) intensity of the prepared phosphor increased linearly with increases in the mechanical load. The ML spectra were similar to the photoluminescence (PL), which indicates that ML is emitted from the same emitting center of Eu²⁺ ions as PL. Copyright © 2014 John Wiley & Sons, Ltd.     

A novel red phosphor Ca2YNbO6:Eu3+ for WLEDs

Due to the advantages of good physicochemical properties, thermal stability, and optical properties, double perovskite compounds have received extensive attention. On this basis, a new type of red phosphor, Ca₂YNbO₆:xEu³⁺, was synthesized using a high-temperature solid-phase method. Its phase purity, morphology, elemental composition, absorption spectrum, photoluminescence, thermal stability, and Commission Internationale de l'éclairage (CIE) chromaticity coordinates were thoroughly investigated. The results display that there is no impurity phase in the samples and the convergence factor R_wp = 14.2%; the microscopic particles are uniform and full, and the distribution of each element is uniform. The energy band gap ΔE is between 3.71 eV and 3.65 eV. The luminescence intensity is the best when the doped Eu³⁺ concentration x reaches 0.4, and emits 612 nm red light (⁵D₀→⁷F₂) under 465 nm excitation, and the concentration quenching is attributed to a d–d interaction. The luminescence intensity at 425 K was still 75% of the room temperature luminescence intensity, which indicates that the thermal stability is extremely superior. The CIE chromaticity coordinates (0.6534, 0.3455) of the Ca2YNbO6:0.4Eu³⁺ phosphors are very close to National Television Standards Committee (0.670, 0.330), and the samples have low correlated colour temperature (2656 K) and high colour purity (99.90%). All findings suggest that Ca₂YNbO₆:Eu³⁺ can serve as a substitute for red phosphor in WLEDs.     

Effect of sintering temperature on the luminescence properties of Ca0.8Ba0.2TiO3:Pr3+ red‐emitting phosphor

Nanoparticles with the nominal composition Ca_0.8Ba_0.2Ti0₃:Pr³⁺ were prepared using the sol–gel process. Barium nitrate, 4‐hydrated calcium nitrate and praseodymium oxide were used as raw materials. The structural evolution and decomposition processes of the precursors were investigated by powder X‐ray diffraction, differential thermal analysis and thermogravimetric analysis. Crystalline Ca_0.8Ba_0.2Ti0₃:Pr³⁺ could be obtained at 700°C. The photoluminescence properties of the samples were investigated using excitation and emission spectra. Ca_0.8Ba_0.2Ti0₃:Pr³⁺ nanoparticles showed strong red emission, which could be assigned to the typical ¹D₂→³H₄ transition of Pr³⁺. Furthermore, the study found that sintering temperature and the introduction of Ba²⁺ influence the decay time of persistent luminescence. Copyright © 2014 John Wiley & Sons, Ltd.     

Hydrothermal growth of Zn2SnO4:Eu,Ca for red emission

Zinc stannate (Zn₂SnO₄) and Zn₂SnO₄ codoped with Eu³⁺ and Ca²⁺ (ZTO:Eu,Ca) were synthesized by hydrothermal method and characterized with X‐ray diffraction (XRD), energy‐dispersive X‐ray analysis (EDAX), Raman spectrometer, field emission scanning electron microscopy (FESEM), ultraviolet‐visible (UV‐vis) and photoluminescence (PL) spectrophotometers. PL analysis of Zn₂SnO₄ gives broad defect induced emission in the region 500–750 nm. The crystal structure of Zn₂SnO₄ was retained even with a nominal doping of Eu, Ca and its combination in the Zn₂SnO₄. The Eu³⁺ ions were found to occupy the non‐centrosymmetric sites of the Zn₂SnO₄ and gave emissions at 592, 615 and 702 nm. Zn₂SnO₄:Eu,Ca showed red emission at 615 nm attributed to the electronic transition from the excited state ⁵D₀ → ⁷F₂ of the 4f⁶ configuration of Eu³⁺. Nominal codoping of Eu³⁺ and Ca²⁺ ions promoted the quenching of orange emission from Eu³⁺ in Zn₂SnO₄:Eu,Ca.     

Effect of replacement of Ca by Zn on the structure and optical property of CaTiO3:Eu3+ red phosphor prepared by sol‐gel method

Eu³⁺‐doped calcium titanate red phosphors, Ca_1‐xZn_xTiO₃:Eu³⁺, were prepared by the sol‐gel method. The structure of prepared Ca_1‐xZn_xTiO₃:Eu³⁺ phosphors were investigated by X‐ray diffraction and infrared spectra. Due to the ⁵D₀ → ⁷F_1–3 electron transitions of Eu³⁺ ions, photoluminescence spectra showed a red emission at about 619 nm under excitation of 397 nm and 465 nm, respectively. When zinc was added to the host, the luminescent intensity of Ca_1‐xZn_xTiO₃:Eu³⁺ was markedly improved several fold compared with that of CaTiO₃:Eu³⁺. Ca_0.9Zn_0.1TiO₃:Eu³⁺ also had higher luminescence intensity than the commercially available Y₂O₃:Eu³⁺ phosphors under UV light excitation. Copyright © 2014 John Wiley & Sons, Ltd.     

Luminescence properties of green‐emitting Ca2MgSi2O7:Eu2+ phosphor by a solid‐state reaction method

A europium (Eu)‐doped di‐calcium magnesium di‐silicate phosphor, Ca₂MgSi₂O₇:Eu²⁺, was prepared using a solid‐state reaction method. The phase structure, particle size, surface morphology, elemental analysis, different stretching mode and luminescence properties were analyzed by X‐ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) with energy dispersive X‐ray spectroscopy (EDX), Fourier transform infrared (FTIR) spectroscopy, photoluminescence (PL) and mechanoluminescence (ML). The phase structure of Ca₂MgSi₂O₇:Eu²⁺ was an akermanite‐type structure, which belongs to the tetragonal crystallography with space group P4?2₁m; this structure is a member of the melilite group and forms a layered compound. The surface of the prepared phosphor was not found to be uniform and particle distribution was in the nanometer range. EDX and FTIR confirm the components of Eu²⁺‐doped Ca₂MgSi₂O₇ phosphor. Under UV excitation, the main emission peak appeared at 530 nm, belonging to the broad emission ascribed to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The ML intensity of the prepared phosphor increased linearly with increasing impact velocity. A CIE color chromaticity diagram and ML spectrum confirmed that the prepared Ca₂MgSi₂O₇:Eu²⁺ phosphor would emit green color and the ML spectrum was similar to that of PL, which indicated that ML is emitted from the same center of Eu²⁺ ions. Copyright © 2015 John Wiley & Sons, Ltd.     

Photoluminescence properties of a novel phosphor CaB2O4:Eu3+ under NUV excitation

The new borate phosphor CaB₂O₄:Eu³⁺ was synthesized by solid‐state method and their photoluminescence properties were investigated. The results show that the pure phase of CaB₂O₄ could be available at 900°C, CaB₂O₄:Eu³⁺ phosphor could be effectively excited by the near ultraviolet light (NUV) (392 nm), and the luminescent intensity of CaB₂O₄:Eu³⁺ phosphor reached to the highest when the doped‐Eu³⁺ content was 4 mol%. The emission spectra of CaB₂O₄:Eu³⁺ phosphor could exhibit red emission at 612 nm and orange emission at 588 nm, which are ascribed to the ⁵D₀–⁷F₂ and ⁵D₀–⁷F₁ transitions of Eu³⁺ ions. Copyright © 2009 John Wiley & Sons, Ltd.     

Mechanoluminescence,thermoluminescence, photoluminescence studies on Ca3Y2Si3O12:RE3+ (RE3+ = Dy3+and Eu3+) phosphors

Dy³⁺ and Eu³⁺ activated Ca₃Y₂Si₃O₁₂ phosphors were synthesized by the solid‐state synthesis method. The phosphors were characterized by X‐ray diffraction (XRD), mechanoluminescence (ML), thermoluminescence (TL) and photoluminescence (PL) to determine structure and luminescence. For ML glow curves, only one peak was observed, as only one type of luminescence centre was formed during irradiation. The Ca₃Y₂Si₃O₁₂:Dy³⁺ TL glow curve showed a single peak at 151.55°C and the Ca₃Y₂Si₃O₁₂:Eu³⁺ TL glow curve peaked at 323°C with a small peak at 192°C, indicating that two types of traps were activated. The trapping parameters for both the samples were calculated using Chen's peak shape method. Dy³⁺‐activated Ca₃Y₂Si₃O₁₂ showed emission at 482 and 574 nm when excited by a 351 nm excitation wavelength, whereas the Eu³⁺‐activated Ca₃Y₂Si₃O₁₂ phosphor PL emission spectra showed emission peaks at 613 nm, 591 nm, 580 nm when excited at 395 nm wavelength. When excited at 466 nm, prominent emission peaks were observed at their respective positions with very slight shifts. Copyright © 2015 John Wiley & Sons, Ltd.     

Photoluminescence and thermoluminescence studies of CaAl2O4:Dy3+ phosphor

Calcium aluminate phosphors activated by Dy³⁺ have been prepared by a combustion method at a temperature of 600°C. Photoluminescence (PL) and thermoluminescence (TL) properties of gamma‐irradiated Dy‐doped calcium aluminate were investigated. The PL spectrum shows a broad peak around 488 nm and 573 nm, under 347 nm excitation. Thermoluminescence studies were performed for different concentrations of Dy. Optimum intensity of photoluminescence was found for 0.02 mol% concentration of Dy. It was found that initially the peak TL intensity increases with increasing concentration of Dy in the CaAl₂O₄ host, attains a maximum value for 0.05 mol% concentration and decreases with further increase in the doping concentration due to concentration quenching. Copyright © 2015 John Wiley & Sons, Ltd.     

Influence of Er3+ concentration on the photoluminescence characteristics and excitation mechanism of Gd2O3:Er3+ phosphor synthesized via a solid‐state reaction method

An Er³⁺‐doped phosphor of Gd₂O₃ (Gd₂O₃:Er³⁺) was prepared using a conventional solid‐state reaction method. The structure and particle size were determined from X‐ray powder diffraction measurements. The average particle size of the phosphor was in between 20 and 50 nm. The particle size and structure of the phosphor were further confirmed by transmission electron microscopy (TEM) analysis. Luminescence spectra were recorded under excitation wavelengths of 275, 380, 515 and 980 nm. The visible upconversion and downconversion luminescence spectra of the Gd₂O₃:Er³⁺ phosphor were investigated as a function of Er³⁺ ion concentration. The upconverted emission at 980 nm excitation shows enhanced red emission with respect to green emission as the dopant concentration increased. Similar results were observed for downconversion emission under 275 and 380 nm excitation wavelengths. The mechanisms responsible for populating the ⁴S_3/2 and ⁴ F_9/2 levels, for green and red emissions, respectively, are different for different excitations and for different concentrations of Er³⁺. Copyright © 2014 John Wiley & Sons, Ltd.     

Structural,morphological and steady state photoluminescence spectroscopy studies of red Eu3+‐doped Y2O3 nanophosphors prepared by the sol‐gel method

Europium trivalent (Eu³⁺)‐doped Y₂O₃ nanopowders of different concentrations (0.5, 2.5, 5 or 7 at.%) were synthesized by the sol‐gel method, at different pH values (pH 2, 5 or 8) and annealing temperatures (600°C, 800°C or 1000°C). The nanopowders samples were characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), Fourier transform infrared spectroscopy (FT‐IR) and steady state photoluminescence spectroscopy. The effect of pH of solution and annealing temperatures on structural, morphological and photoluminescence properties of Eu³⁺‐doped Y₂O₃ were studied and are discussed. It was found that the average crystallite size of the nanopowders increased with increasing pH and annealing temperature values. The Y₂O₃:Eu³⁺ material presented different morphology and its evolution depended on the pH value and the annealing temperature. Activation energies at different pH values were determined and are discussed. Under ultraviolet (UV) light excitation, Y₂O₃:Eu³⁺ showed narrow emission peaks corresponding to the ⁵D_0–⁷F_J (J = 0, 1, 2 and 3) transitions of the Eu³⁺ ion, with the most intense red emission at 611 assigned to forced electric dipole ⁵D₀→⁷F₂. The emission intensity became more intense with increasing annealing temperature and pH values, related to the improvement of crystalline quality. For the 1000°C annealing temperature, the emission intensity presented a maximum at pH 5 related to the uniform cubic‐shaped particles. It was found that for lower annealing temperatures (small crystallite size) the CTB (charge transfer band) position presented a red shift. Copyright © 2015 John Wiley & Sons, Ltd.     

Optical analysis of RE3+ (RE = Pr3+, Er3+ and Nd3+):cadmium lead boro tellurite glasses

This article reports on the optical characterization of Pr³⁺‐, Er³⁺‐ and Nd³⁺‐doped cadmium lead boro tellurite (CLBT) glasses prepared using the melt quenching method. The visible–near infrared (Vis–NIR) absorption spectra of these glasses were analyzed systematically. On measuring the NIR emission spectra of Er³⁺:CLBT glasses, a broad emission band centered at 1536 nm (⁴I_13/2 → ⁴I_15/2) was observed, as were three NIR emission bands at 900 nm (⁴F_3/2 → ⁴I_9/2), 1069 nm (⁴F_3/2 → ⁴I_11/2) and 1338 nm (⁴F_3/2 → ⁴I_13/2) from Nd³⁺:CLBT glasses and an NIR emission band at 1334 nm (¹G₄ → ³H₅) from Pr³⁺:CLBT glasses at an excitation wavelength (λ_ex) of 514.5 nm (Ar⁺ laser). Copyright © 2016 John Wiley & Sons, Ltd.     

Ca3(PO4)2:Eu3+ phosphor preparation with different morphologies and their fluorescence properties

Ca₃(PO₄)₂:Eu³⁺ phosphor was prepared using a facile chemistry method in the presence of surfactants. The effects of surfactants on the morphology and photoluminescence properties of Ca₃(PO₄)₂:Eu³⁺ phosphor were investigated. The morphology of the phosphor was significantly influenced by the surfactants employed. When nonionic surfactant glyceryl monostearate and anionic surfactant sodium dodecylbenzene sulfonate were employed, the phospor powders are composed of a large number of homogeneous spherical particles with sizes of 0.3–0.6 µm and 2–3 µm, respectively. By contrast, when cationic surfactant cetyltrimethylammonium bromide was used, the morphology of the phosphor is completely different. The product is an excellent cuboid, and the phosphor prepared with 2.5 mmol cetyltrimethylammonium bromide showed higher luminescent intensity than phosphors prepared with the other two types of surfactants. Copyright © 2013 John Wiley & Sons, Ltd.     

Insights into the discrepant luminescence for BaSiO3:Eu2+ phosphors prepared by solid‐state reaction and precipitation reaction methods

Two synthesis routes, solid‐state reaction and precipitation reaction, were employed to prepare BaSiO₃:Eu²⁺ phosphors in this study. Discrepancies in the luminescence green emission at 505 nm for the solid‐state reaction method sample and in the yellow emission at 570 nm for the sample prepared by the precipitation reaction method, were observed respectively. A detail investigation about the discrepant luminescence of BaSiO₃:Eu²⁺ phosphors was performed by evaluation of X‐ray diffraction (XRD), photoluminescence (PL)/photoluminescence excitation (PLE), decay time and thermal quenching properties. The results showed that the yellow emission was generated from the BaSiO₃:Eu²⁺ phosphor, while the green emission was ascribed to a small amount of Ba₂SiO₄:Eu²⁺ compound that was present in the solid‐state reaction sample. This work clarifies the luminescence properties of Eu²⁺ ions in BaSiO₃ and Ba₂SiO₄ hosts.     

Synthesis and photoluminescence characteristics of Sm3+‐doped Bi4Si3O12 red‐emitting phosphor

A series of novel red‐emitting Sm³⁺‐doped bismuth silicate phosphors, Bi₄Si₃O₁₂:xSm³⁺ (0.01 ≤ x ≤ 0.06), were prepared via the sol–gel route. The phase of the synthesized samples calcinated at 800 °C is isostructural with Bi₄Si₃O₁₂ according to X‐ray diffraction results. Under excitation with 405 nm light, some typical peaks of Sm³⁺ ions centered at 566, 609, 655 and 715 nm are found in the emission spectra of the Sm³⁺‐doped Bi₄Si₃O₁₂ phosphors. The strongest peak located at 609 nm is due to ⁴G_5/2–⁶H_7/2 transition of Sm³⁺. The luminescence intensity reaches its maximum value when the Sm³⁺ ion content is 4 mol%. The results suggest that Bi₄Si₃O₁₂:Sm³⁺ may be a potential red phosphor for white light‐emitting diodes. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and luminescence of Eu3+‐doped in triple phosphate Ca8MgBi(PO4)7 with whitlockite structure

Triple whitlockite‐type structure‐based red phosphors Ca₈MgBi_1?x(PO₄)₇:xEu³⁺ (x = 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80 and 1.00) were synthesized by a conventional solid‐state reaction route and characterized by their X‐ray crystal structures. The X‐ray diffraction (XRD) patterns, Fourier transform infrared spectra, morphologies, photoluminescence spectra, UV/Vis reflectance spectra, decay times and the International Commission on Illumination (CIE) chromaticity coordinates of Ca₈MgBi_1?x(PO₄)₇:xEu³⁺ were analyzed. Eu‐doped Ca₈MgBi(PO₄)₇ phosphors exhibited strong red luminescence with peaks at 616 nm due to the ⁵D₀ → ⁷ F₂ electric dipole transition of Eu³⁺ ions after excitation at 396 nm. The UV/Vis spectra indicated that the band gap of Ca₈MgBi_0.30(PO₄)₇:0.70Eu³⁺ is larger than that of Ca₈MgBi(PO₄)₇. The phosphor developed in this study has great potential as a red‐light‐emitting phosphor for UV light‐emitting diodes. Copyright © 2015 John Wiley & Sons, Ltd.     

Electrospinning preparation and photoluminescence properties of Y3Al5O12:Tb3+ nanostructures

Novel nanostructures of Y₃Al₅O₁₂:Tb³⁺ (denoted as YAG:Tb³⁺ for short) nanobelts and nanofibers were fabricated by calcination of the respective electrospun PVP/[Y(NO₃)₃ + Tb(NO₃)₃ + Al(NO₃)₃] composite nanobelts and nanofibers. YAG:Tb³⁺ nanostructures are cubic in structure with a space group of I_a3d. The thickness and width of the YAG:7%Tb³⁺ nanobelts are respectively ca. 125 nm and 5.9 ± 0.3 µm, and the diameter of YAG:7%Tb³⁺ nanofibers is 166.0 ± 20 nm (95% confidence level). The YAG:Tb³⁺ nanostructures emit predominantly at 544 nm from the energy levels transition of ⁵D₄ → ⁷ F₅ of Tb³⁺ ions under the excitation of 274‐nm ultraviolet light. It was found that the optimum doping molar concentration of Tb³⁺ ions for YAG:Tb³⁺ nanostructures was 7%. Compared with YAG:7%Tb³⁺ nanofibers, YAG:7%Tb³⁺ nanobelts exhibit a stronger photoluminescence (PL) intensity under the same doping concentration. Commission International de l'Eclairage (CIE) analysis demonstrates that the emitting colors of YAG:Tb³⁺ nanostructures are located in the green region and color‐tuned luminescence can be obtained by changing the doping concentration of Tb³⁺ and morphologies of the nanostructures, which could be applied in the field of optical telecommunication and optoelectronic devices. The possible formation mechanisms of YAG:Tb³⁺ nanobelts and nanofibers are also proposed. Copyright © 2014 John Wiley & Sons, Ltd.     

念珠藻对岩溶水中 Ca2＋、HCO－3利用效率实验研究

岩溶碳汇过程中石灰石溶解将大气/土壤中 CO 2转移到水体形成 HCO －3促进水生藻类的生长.该文为了研究水生藻类光合作用将岩溶水中无机碳转化为有机碳的效率,采用从岩溶水生生态系统中筛选出的念珠藻作为研究对象,探讨在封闭体系中藻细胞光合作用时对典型岩溶水中 Ca2＋、HCO －3利用、藻细胞生物量的变化与 Ca2＋、HCO －3的利用关系以及体系 pH、DO 的变化.结果表明：念珠藻通过光合作用能吸收利用岩溶水中27．38％的 Ca2＋,同时将29．54％的 Ca2＋通过物理化学作用以“藻体-CaCO 3”复合体形式沉淀而返回到无机环境.pH 漂移实验表明念珠藻光合作用过程中先利用水体中游离 CO 2,然后以岩溶水中 HCO －3为碳源.由于水体中岩溶作用产生的 HCO －3不断被光合作用利用而引起体系 pH 和 DO 的升高.念珠藻光合作用将岩溶水中65％的 HCO －3转化为稳定化合物,其中18．46％以胞外 CaCO 3形式被沉淀,81．54％被藻类转化为有机物,表现为净碳汇效应.     

Thermal quenching of luminescence of LiSr4(BO3)3:Eu2+ orange‐emitting phosphor

An orange‐emitting phosphor, Eu²⁺‐activated LiSr₄(BO₃)₃, was synthesized using the conventional solid‐state reaction. The photoluminescence excitation and emission spectra, and temperature dependence of the luminescence intensity of the phosphor were investigated. The results showed that LiSr₄(BO₃)₃:Eu²⁺ could be efficiently excited by incident light of 250–450 nm, and emits a strong orange light. With increasing temperature, the emission bands of LiSr₄(BO₃)₃:Eu²⁺ show an abnormal blue‐shift with broadening bandwidth and decreasing emission intensity. Copyright © 2013 John Wiley & Sons, Ltd.